The present invention relates generally to material handling equipment and more particularly to an improved self-leveling linkage for controlling the position of a bucket supported on a boom.
In conventional earth moving equipment, such as bucket loaders, one or more lift arms are pivotally carried on a tractor with a bucket pivoted on the free end of the lift arms. Generally, the lift arms are raised and lowered on the tractor by a hydraulic cylinder having fluid supplied thereto through a control valve while the bucket is pivoted on the end of the lift arms through an additional hydraulic cylinder having fluid supplied thereto through a further control valve.
In normal operation, the bucket is positioned in a "dig" position and is forced into a pile of material by forward movement of the tractor. The bucket is then pivoted or rolled back on the boom or lift arms for the tractor with sufficient force to break out the mass of material within the bucket from the remainder of the pile. Subsequently, the lift arms are elevated a sufficient distance to raise the bucket above the ground and the tractor is driven to some other location. Upon reaching the subsequent location, the bucket is pivoted to a "dumping" position where the contents are discharged, after which the operation is repeated.
In an operation such as this, it is important that the bucket be maintained at a "level position" while the tractor is driven from the first location to the second to prevent the material or contents from being spilled. While various self-leveling control mechanisms have been proposed for preventing the bucket from being pivoted beyond a predetermined maximum roll-back position or for maintaining the bucket at a level position, there are problems associated with the devices heretofore known.
For example, if the tractor is inoperative with the lift arms in the raised position, hydraulic fluid leakage may occur both in the bucket cylinder and loader control valve. Since the center of gravity of a leveled loader bucket in the raised position is normally rearward of the bucket pivot, the bucket will rollback when the hydraulic system is inoperative and leakage occurs. With known self-leveling linkage assemblies, this has resulted in bent or ruined linkage elements. Thus, there has been a need for an improved self-leveling linkage assembly which overcomes the problems associated with prior constructions.